Polyglycidates (also referred to herein as epoxy compounds) generally constitute a class of compounds having at least two glycidyl groups, the reactive moiety in each glycidyl group being the epoxy group.
Many epoxy compounds are commercially available for use in epoxy resin systems including N,N,N',N',-tetraglycidyl-4,4'-methylene dianiline, having the structure ##STR2## This material is made by reacting an excess of epichlorohydrin with methylene dianiline. It is available commercially as MY-720 from Ciba Geigy Corp., Ardsley, N.Y. and consists of about 70% by weight of the above tetraglycidate, the remainder being oligomers and triglycidates.
Another commonly used epoxy compound is made by reacting bisphenol A with epichlorohydrin. Commercially available resins made from this reaction contain the structure ##STR3## and include DER 331 from Dow Chemical and EPON.RTM. 828 (registered trademark) from Shell.
Epoxy groups are reactive to amine and hydroxyl functionalities and can thus be copolymerized (i.e. cured) with compounds containing such functionalities to make epoxy resin systems. Generally polyamines are favored as curing agents although polyhydroxy curing agents are also well known. The epoxy compounds can be reacted with one or more curing agents such that they are crosslinked, thereby finding use as structural adhesives or as encapsulating materials for electronic components.
Epoxy resin systems are often used in prepregs, ready-to-mold materials comprising fibrous reinforcement impregnated with uncured or partially cured epoxy resin systems. Prepregs can be assembled into a final part (such as an airplane wing) and fully cured (C-staged) to form a finished product. Such prepregs find wide use in the aircraft and aerospace industries.
Key properties of epoxy resin systems are tensile properties and moisture sensitivity. High tensile strength is desirable in, for example, structural adhesives. Low moisture sensitivity is also desirable since it leads to improved performance under hot/wet conditions.
Most advanced composites are fabricated from prepreg. Resin systems containing an epoxy compound such as MY-720 and aromatic amine hardener are often used in prepreg since they possess the balance of properties required for this material. State-of-the-art epoxy/carbon fiber composites have high compressive strengths, good fatigue characteristics, and low shrinkage during cure. However, since most epoxy formulations used in prepreg are brittle, these composites have poor impact resistance. In addition, epoxy formulations absorb moisture which reduces their high temperature properties and affects their dimensional stability.
Thus, new epoxy compounds which could be used to make epoxy resin systems which improve such desirable physical and mechanical properties, relative to present state-of-the-art epoxy systems, would be a useful addition to the structural adhesive, airplane, aerospace, and other like art areas.